It is a commonplace that the war beginning in 1939 is a continuation of the one which ended in 1918, much as European conflicts of the 18th century (such as the Seven Years' War) were often a return to unfinished business. In many respects the commonplace is true, and it is reflected in everyday vocabulary. No other wars are numbered I and II, like kings in a line of succession or blockbuster films in a series.

The idea of a progression from World War I to World War II is unavoidable, and several factors make it so.

The same nation, Germany, is the participant most actively responsible for each of the two wars. In 1914 this had been a panic reaction, through fear of losing advantage if not moving first. In 1939 it is the deliberate result of the policy of one man, Adolf Hitler.

That policy can in many respects be traced back to the after-effects of World War I. Hitler, in his vengeful and expansionist plans for Germany, is able to play on German resentment of the terms imposed by the Treaty of Versailles. He is helped also by another undercurrent from 1918 - the feeling that Germany was not really defeated at the end of that war. Her politicians capitulated before a single foreign soldier had trodden on German soil. If the match were replayed, the result could be different.

This sense of aggrieved military self-confidence is to a large extent supported by a striking fact. For eight years of the 20th century (1914-18, 1941-5) Germany almost single-handedly holds at bay the three other great European powers, Russia, France and Britain, united against her and for much of the time aided by the USA.

Yet within the broad pattern of continuity there are differences. The most profound of these lies in the reasons for the two wars. The causes of World War I are notoriously hard to discern, shrouded in the posturing of imperial powers. It has come to seem the most pointless of conflicts, and until that time the most wasteful of human life.

By contrast World War II, even more costly in terms of lives lost, is the war with the clearest moral purpose - to curtail the apparently boundless aggression of Hitler, and to destroy the most successful of the extremist creeds of the 1930s, Fascism.

This relates to another distinction. Germany and Austria (linked from 1938 by the Anschluss) have very different partners the second time round, in Italy and Japan. Italy and Germany share the creed of Fascism, and distant Japan is like Germany in being an aggressive and authoritarian military society. Even so, the three make strange bedfellows in the group which is formed in 1936 and becomes known as the Axis.

The Axis Powers: 1936

In October 1936 an agreement between Germany and Italy establishes much common ground in foreign policy. The arrangement is described by Hitler (in conversation with Galeazzo Ciano, Mussolini's son-in-law and foreign secretary) as an alliance between the two most vigorous European nations, rearming faster than any others and capable together of defeating Great Britain if necessary.

Mussolini has, this very summer, overwhelmed Ethiopia and proclaimed a new Italian empire. Hitler has been the first head of state to recognize this dubious enterprise. Mussolini now accidentally gives the new alliance its familiar name, describing it as an axis 'round which all those European states which are animated by a desire for collaboration and peace may work together'.

Before the end of the year the group has a new adherent, animated no more than Italy or Germany by a desire for peace. Japan has recently seized much of northern China and has set up the puppet state of Manchoukuo (the recognition of which is one of the clauses in the 'axis' agreement).

In this region Japan has a hostile neighbour in a nation which is also geographically close to Germany and is profoundly loathed by Hitler. Germany in the extreme west and Japan in the extreme east share a hatred and fear of the USSR. This is the basis for the agreement reached between the two nations in November 1936. It is called the Anti-Comintern Pact, to present it as an alliance against international communism rather than a single country.

Hitler sees this as the beginning of a military alliance between anti-Communist nations, and it is German policy to tie the knot tighter (culminating in the Tripartite Pact with Italy signed in September 1940). The collaboration within the trio is never very close. Hitler rarely takes Mussolini into his confidence on strategic matters, and Japan operates in a world of its own. Germany enters World War II without the involvement of either of its Axis partners, and ends it with only one of them as an ally.

But in the years after the establishment of the Axis, in the late 1930s, it is convenient for Hitler to have such an alliance while he pushes to the limit the patience of the other European powers - benefiting greatly from their instinct that aggression may be calmed by appeasement.

Expansion and appeasement: 1935-1939

The policy which becomes known as appeasement (the belief that compromise with Europe's fascist dictators will provide the best chance for peace) is associated particularly with the British prime minister Neville Chamberlain. But it already characterizes the foreign policy up to 1937 of his predecessor, Stanley Baldwin. And it is, to a lesser extent, the policy also of the government in France.

As the two major European powers in the League of Nations, Britain and France inevitably have to play the leading role in trying to keep Hitler and Mussolini in check.

A conciliatory attitude, partly made necessary by the lack of readiness in each nation for another war, is evident as early as 1935. In this year Samuel Hoare and Pierre Laval, foreign ministers of the two countries, concoct a peace plan which would allow Italy to annexe large slices of Ethiopia (an independent state, recently invaded by Italian armies).

The plan is rejected, but its very existence encourages Mussolini to complete his conquest of Ethiopia. And this de facto state of affairs is soon accepted by an increasingly enfeebled League of Nations.

Earlier in the same year there has been another affront to the League's authority. In March 1935 Hitler informs Britain and France that he is creating an air force, is launching a major programme of military and naval rearmament, and is introducing conscription.

These plans directly contravene the terms of the treaty of Versailles. But in June, to the outrage this time of France, Hoare establishes an Anglo-German Naval Agreement, tacitly accepting the naval aspect of Hitler's plans in return for a pact that German strength at sea will not exceed 35% of the combined fleets of Britain and the Commonwealth.

In March 1936 Hitler makes his first military move in defiance of existing treaties. He marches his troops into the Rhineland, a region permanently demilitarized under the terms agreed at Versailles. At the same time he declares (in what is to become a recurring pattern) that this is his last territorial claim.

The Spanish Civil War, beginning in July 1936, absorbs much of Europe's attention over the next two years (and provides Hitler's new forces with their first unofficial outing). But from 1938 the German dictator's provocative moves come at an ever increasing pace, each of them taking to the brink the good faith of the appeasers.

On March 12 he marches into Austria to reunite the ancient German Reich, an event known as the Anschluss (literally 'joining on'). On the previous day he assures the world that he has no designs on Czechoslovakia.

The very next month, in April, he develops a secret plan to annexe the western part of Czechoslovakia, the Sudetenland. He is considerably helped in this ambition by the principles of Versailles, for the region has a predominantly German population. Many of these Germans are already Nazi sympathisers. It is easy to argue, against Czech interests, that the principle of self-determination gives these people the right to merge with Germany. During the summer of 1938 Hitler threatens the Czech government at the diplomatic level, while massing troops on the border.

Chamberlain flies from London to confer with Hitler, on September 15 and 22, but by September 27 it seems certain that Hitler's forces will cross the Czech border. France has a defensive treaty with Czechoslavakia. Britain would have to support France. The result would be war.

On September 27 Chamberlain broadcasts to the British people, expressing his appalled dismay at being dragged into the affairs of such a 'Faraway country'. The next day he sends a telegram to Hitler, offering to fly again to Germany to discuss the peaceful transfer of the Sudetenland. Hitler postpones the invasion, planned for September 28, and invites Chamberlain, Daladier (the French premier since April) and Mussolini to an immediate meeting in Munich.

Munich and after: 1938-1939

The discussion in Munich between Hitler, Chamberlain, Daladier and Mussolini lasts a little over twelve hours, beginning in the middle of the day on September 29 and ending with the signing of an agreed document at 1.30 a.m. on September 30. Though the dismantling of their country is under discussion, Hitler refuses to allow any Czech representative to take part. Two Czech diplomats sit in a nearby hotel, effectively waiting to be told what has been decided.

The conclusion is all that Hitler would wish. The Sudeten areas are to be ceded to Germany during the next ten days. Thereafter plebiscites, organized by the four Munich powers and Czechoslovakia, will reveal exactly where the new border should run.

Before boarding his plane, later on September 30, Chamberlain has another meeting with Hitler in which he asks him to sign a joint declaration. This is the document which Chamberlain waves in the air for the cameras on his return to Britain, stating that he has brought back from Germany 'peace for our time... peace with honour'.

The text above Hitler's signature, on which Chamberlain bases his optimism, declares a determination to remove possible sources of difference between countries 'and thus to contribute to assure the peace of Europe'. Chamberlain's hope is that the sacrifice of the Sudetenland has preserved not only peace but the rest of Czechoslovakia.

The occupation of Sudetenland brings some 3.5 million people within Nazi Germany, 75% of them German and 25% Czech. But in the event these Czechs are no more unfortunate than their compatriots elsewhere. Three weeks after signing Chamberlain's document, Hitler orders the German army to prepare for a move into the rest of Czechoslovakia. The invasion comes in March 1939. Hitler, in Prague, declares that Bohemia, Moravia and Slovakia are now under the protection of the German Reich.

But such a brutal betrayal of the Munich agreement transforms the appeasers. When it becomes evident that Poland is the next likely victim, Britain and France are suddenly resolute.

Danzig and the Polish corridor: 1938-1939

At the very moment of the Munich agreement the Polish government presents its own demand for a slice of Czechoslovakia. There is logic to the claim. If the Sudetenland with its largely German population is to be annexed by Germany, then there is a clear case for the rich industrial area of Teschen Silesia, inhabited mainly by Poles, to be transferred to Poland. On the day the Munich agreement is announced, 30 September 1938, Poland asserts this claim - not for the first time, but now it is instantly acceded to by Czechoslavakia.

Unfortunately the ethnic-majority argument has dangerous implications for Poland herself, confronted by a Hitler increasing day by day in confidence.

The great port of Gdansk (in Polish) or Danzig (in German) has long been a bone of contention between Polish and German interests. Though first brought to prominence by the Hanseatic merchants, the city and its hinterland (eastern Pomerania, or in its Polish name Pomorze) have historically been part of Poland. But from time to time they have been seized by Germans - first by the Teutonic knights in 1308 - and in recent times they have again been German, from the late 18th-century partitions of Poland until the end of World War I.

In 1919 the treaty of Versailles restores Pomorze to Poland and gives Danzig, with its almost entirely German population, the status of a free city within the borders of Poland.

This arrangement is probably unworkable at the best of times, and more so from the mid-1930s when Danzig has an elected Nazi city council. Moreover in this area the provisions of Versailles provide a further cause for German grievance. In returning Pomorze to Poland, and restoring her historical access to the sea at Danzig, the treaty has the effect of severing the province of East Prussia from the rest of Germany.

Pomorze becomes known in the terminology of the 1920s as the Polish corridor, linking Poland and the sea. Hitler now demands a more literal German corridor - a narrow strip of German territory through Poland to East Prussia. Together with this goes his claim to bring Danzig within the Reich.

Both claims are pressed by Hitler with new vigour in October 1938, within days of his winning the Sudetenland from Czechoslovakia. The Polish government firmly rejects the German demands. Unlike unfortunate Czechoslovakia, this stance wins a positive response from the western powers.

In March 1939 Neville Chamberlain, speaking with the approval of both France and the USSR, gaurantees help to Poland if her independence is threatened. In April Hitler abrogates his own ten-year nonaggression treaty with Poland, signed in 1934, and secretly orders his army to prepare for a Polish invasion. In May France commits herself to military action against Germany if a conflict begins. But then, in August, Hitler produces a diplomatic bombshell.

Ribbentrop-Molotov Pact: 1939

In August 1939 a Franco-British military mission is in Moscow trying to persuade Stalin to commit to a treaty for the defence of Poland. Little progress is made, ostensibly because the Poles are refusing to allow Soviet troops to cross their territory to attack Germany. But there is another hidden reason which soon becomes apparent.

The Soviet Union and Communism have always been twin forces of demonic evil in Hitler's oratory, but he now proves himself happy to sup with the devil for a very real strategic advantage. It is important to his plans that he shall not be distracted by a major war on his eastern front. In August he opens negotiations with Stalin. Poland is his bait.

Stalin, invited by the western powers to join an alliance which will almost certainly involve him in a costly war against Germany for no very evident benefit, now finds himself offered a more attractive option - inactivity and a sizable increase in his territory.

It takes the Russian dictator little time to choose. The world is astonished on August 21 by the announcement from Berlin that Ribbentrop is flying to Moscow to sign a nonaggression pact with his opposite number, the Russian foreign minister Molotov. This sudden friendship of two implacable enemies would seem less inexplicable if people knew of the secret protocol which accompanies the pact.

The protocol agrees a new set of international boundaries. As modified slightly in a second visit by Ribbentrop to Moscow, in September, it acknowledges Germany's approval of the Russian annexation of the independent nations Finland, Estonia, Latvia and Lithuania (should any such opportunity occur). And it establishes an agreed division of Poland between Germany and Russia.

With this much achieved, Hitler is ready to take his next step - launched, for propaganda purposes, with a grisly little charade.